Duct with transition section for turbine exhaust

ABSTRACT

An exhaust duct for a gas turbine includes a transition section having an inlet for receiving turbine exhaust gas and a relatively larger outlet for interfacing with an auxiliary section housing an auxiliary device. The transition section has an interior surface extending from the inlet to the outlet. The interior surface has a segment generally adjacent to the inlet that is curved to induce a Coanda effect in which the turbine exhaust gas is caused to flow along said curved surface and to expand for distribution of the turbine exhaust gas over the auxiliary device in the auxiliary section.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of U.S. application Ser. No. 12/986,657, filed Jan. 7, 2011, the entirety of which is incorporated by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to the distribution of gas through a turbine exhaust duct as the gas moves from a gas turbine exhaust to a larger area necessary to accommodate auxiliary devices, such as catalyst(s), silencer panel(s), and perforated plate(s).

BACKGROUND OF THE DISCLOSURE

Catalytic reduction systems are used to remove pollutants such as carbon monoxide (CO) and nitrogen oxides (NOx) from combustion products of gas turbines used in power generation. The catalysts used in such catalytic reduction systems are designed to be used within a specific range of air flow velocities. The catalyst is typically presented in a large vertical porous structure located in an exhaust duct or conduit. The porous structure allows exhaust gases to pass through in proximity to catalyst elements. Other designs of catalyst trays may also be used. To accommodate the catalyst, a significant expansion of duct cross-sectional area is required as compared to the cross sectional area of the turbine exhaust. Symmetric or asymmetric transition ducts may be required to accommodate the large catalysts, depending on available space, equipment orientation, and other factors associated with a gas turbine unit.

A conventional prior art gas turbine and gas turbine exhaust duct, as shown in FIGS. 1 and 2, uses a straight wall transition duct with flow redistribution devices, such as perforated plates, that redistribute gas turbine exhaust gas flow by creating local obstructions or areas of higher pressure drop. This method can be expensive as it requires long duct lengths and high system pressure drops to achieve the needed redistribution.

Example prior art gas turbine unit 10 is disclosed in greater detail as follows.

Referring now to FIGS. 1-3, shown is a prior art gas turbine unit designated generally 10 (FIG. 1). Example gas turbine unit 10 is a simple cycle SCR unit. However, the invention described herein may be used with other types of gas turbine units, including emission reduction systems, units with heat recovery steam generation systems or other types of gas turbine units. Gas turbine unit 10 includes inlet air filtration system 12 which feeds air to gas turbine 14. Gas turbine exhaust exits from gas turbine 14 through gas turbine exhaust outlet 16. Gas turbine exhaust flows into inlet 18 of gas turbine exhaust duct 20 (FIGS. 1 and 2), whereupon gas turbine exhaust is directed to exhaust stack 22.

As shown in FIG. 2, gas turbine exhaust gas 24 can be seen entering inlet 18 of gas turbine exhaust duct 20. In exemplary gas turbine exhaust duct 20 of FIGS. 1 and 2, gas turbine exhaust duct 20 supports and encloses vertical CO catalyst 26 (FIGS. 2, 3), vertical ammonia injection grid 28 (FIG. 2) and vertical SCR (selective catalytic reduction) catalyst 30 (FIG. 2). Gas turbine exhaust duct 20 is made up of a transition section 32 (FIGS. 1-3) which transitions from a relatively small inlet 18 to a relatively larger area, i.e., expanded area 33 (FIGS. 1, 2) that accommodates catalysts 26 and/or 28 and/or 30 or other suitable catalysts.

Referring now primarily to FIG. 3, shown is an enlarged isometric view of prior art transition section 32. Transition section 32 is made up of top wall 34, bottom wall 36, first side wall 38, and second side wall 40. It can be seen that walls 34-40 converge to form inlet 18 on a first end and expand outwardly to define an outlet end 42. Perforated plate redistributive device for housing catalyst 26 is visible within transition section 32.

In the prior art design of FIG. 3, turbine exhaust gas must be forced by some means into the expanded area. This often requires large pressure drops and long duct lengths as the gas flow tends to form eddies and does not naturally follow the angle of the duct walls.

SUMMARY OF THE INVENTION

In one aspect, an exhaust duct for a gas turbine generally comprises a transition section having a top wall, a first side wall, a second side wall, and a bottom wall. The transition section has an intake for receiving turbine exhaust gas and a relatively larger outlet area for interfacing with a larger duct area. At least one of the top wall, the first side wall, the second side wall and the bottom wall has a first segment adjacent to the intake that defines a first curved surface that increases in slope toward the outlet area, and a second segment adjacent to the outlet area that defines a second curved surface that decreases in slope toward the outlet area and levels off at the outlet area to interface with the larger duct area.

In another aspect, an exhaust duct for a gas turbine generally comprises a transition section having an inlet for receiving turbine exhaust gas and a relatively larger outlet. The transition section includes at least one wall defining an interior surface having a concave segment generally adjacent to the inlet and extending away from the inlet, and a convex segment generally adjacent to the outlet extending toward the outlet.

In yet another aspect, an exhaust duct for a gas turbine generally comprises a transition section having an inlet for receiving turbine exhaust gas, and a relatively larger outlet for interfacing with an auxiliary section housing an auxiliary device. The transition section has an interior surface extending from the inlet to the outlet. The interior surface has a segment generally adjacent to the inlet that is curved to induce a Coanda effect in which said turbine exhaust gas is caused to flow along the curved surface and to expand for distribution of the turbine exhaust gas over the auxiliary device in the auxiliary section.

Other features will be in part apparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a prior art simple cycle SCR gas turbine unit of the type that may be fitted with the duct transition section of the invention;

FIG. 2 is an enlarged elevation view of a prior art turbine exhaust duct of FIG. 1 having a transition section;

FIG. 3 is an enlarged isometric view of a prior art exhaust conduit transition section of FIGS. 1 and 2 having perforated plates and straight angled walls;

FIG. 4A is an elevation view of a turbine exhaust duct having a first embodiment of a transition section of the present invention;

FIG. 4B is an enlarged elevation view of the transition section in FIG. 4A

FIG. 4C is an isometric view of a curved wall transition section of the invention depicting one wall, i.e., a top wall, of the transition section curved to induce a Coanda effect;

FIG. 5 is a plan view of another embodiment of a curved wall transition section depicting curved sidewalls of a transition section of an exhaust conduit to induce a Coanda effect;

FIG. 6 is a plan view of another embodiment of a curved wall transition section depicting one curved sidewall of a transition section of an exhaust conduit to induce a Coanda effect;

FIG. 7 is an elevation view of another embodiment of a curved wall transition section depicting an additional embodiment of a curved upper wall of a transition section of an exhaust conduit to induce a Coanda effect;

FIG. 8 is an elevation view of another embodiment of a curved walled transition section depicting curved upper and lower walls of a transition section of an exhaust conduit to induce a Coanda effect;

FIG. 9 is an elevation view of another embodiment of a curved wall transition section depicting an additional embodiment of a curved upper wall of a transition section of an exhaust conduit that curves into the gas flow before curving away to induce a Coanda effect; and

FIG. 10 is a streamline plot of a transition section constructed in accordance with the teachings of the embodiment illustrated in FIGS. 4A and 4B using ANSYS CFX software.

Corresponding reference characters indicate corresponding parts throughout the drawings.

DETAILED DESCRIPTION OF THE DRAWINGS

The present disclosure relates to an exhaust duct for a turbine (e.g., a gas turbine). In particular, the exhaust duct of the present disclosure includes a transition section having an inlet (or intake) for receiving exhaust gas from the turbine, and an outlet having a relatively larger opening (i.e., greater open area than the inlet) for interfacing, in fluid communication, with an auxiliary section, which encloses an auxiliary device (e.g., one or more of catalyst(s), such as a CO catalyst and an SCR catalyst, silencer panel(s), ammonia injection grid(s), and perforated plate(s)). The transition section has at least one curved interior surface that induces a Coanda effect as exhaust gas flows from the inlet toward the outlet and into the auxiliary section, such that the flowing exhaust gas generally “follows” the curved interior surface, without substantial flow separation. This curved interior surface, by inducing the Coanda effect, promotes expansion and redistribution of the exhaust gas inside the transition duct as the gas flows toward the larger outlet and into the auxiliary section.

It is believed, based on computational fluid dynamic (CFD) modeling, that the curved interior surface more efficiently promotes redistribution of the exhaust gas in a shorter transition section, as compared to a conventional straight wall transition section using one or more conventional perforated plates, and also reduces the pressure drop in the exhaust duct (by as much as 15%) as compared to the conventional perforated plate system. It is further believed that in most, if not all applications, the turbine operates more efficiently with a reduced pressure drop in the exhaust duct. It is believed that the curved interior surface promotes expansion and redistribution of the exhaust gas to such an extent that, in at least some applications, a perforated redistribution plate—as used in conventional exhaust ducts—is not needed to effectively expand and redistribute the exhaust gas. Moreover, if a perforated redistribution plate is used, the sizes of the openings in the redistribution plate can be greater than the openings in redistribution plates of a conventional system to further reduce the pressure drop in the exhaust duct.

Referring now to FIG. 4A, a first embodiment of an exhaust duct is generally indicated at 120. The exhaust duct includes a transition section, generally indicated at 122, an auxiliary section 124 having a larger duct area immediately downstream of the transition section and housing an auxiliary device 126 (e.g., one or more of catalyst(s), such as a CO catalyst and an SCR catalyst, silencer panel(s), ammonia injection grid(s), and perforated plate(s)), a vertical breech section 128 immediately downstream of the auxiliary section, and a vertical stack section 130 immediately downstream of the vertical breech section. The auxiliary section 124, the vertical breech section 128, and the vertical stack section 130 are generally known in the art and therefore will not be described in detail herein. Each of the sections 122, 124, 128, 130 may be formed separately from one another and connected to one another, such as by welding and/or fasteners, to form the exhaust duct. Each section 122, 124, 128, 130 may be of a single, unitary construction or may be formed from separate parts connected to another, such as by welding and/or fasteners. Most of the external structural supports of the exhaust duct 120 have been removed for purpose of clarity and ease of illustration.

As shown best in FIG. 4B, the transition section 122 has an intake or inlet 134, with a central axis A, for receiving exhaust gas from the turbine (or a diffuser, as explained below), and an outlet 136 that is larger than the inlet (i.e., has a greater open area than the inlet) for interfacing, in fluid communication, with the auxiliary section 124. In one example, the ratio of the open area of the inlet 134 to the open area of the outlet 136 may be greater than or equal to about 1:2.3, such as from about 1:2.3 to about 1:25, or from about 1:10 to about 1:20, or from about 1:13 to about 1:18. The transition section 122 has a connecting flange 138 generally adjacent the inlet 134 for direct securement to a connector (not shown) of either the turbine (e.g., a gas turbine) or a diffuser (if present) downstream of the turbine. (In FIG. 4A, box 140 schematically represents either the turbine or a diffuser, if one is used.) As such, the transition section 122 is connected directly to either the gas turbine or the diffuser, both indicated at 140 in FIG. 4A. The transition section 122 also includes an expansion joint 142 to accommodate linear expansion of the turbine 140 and/or the diffuser 140 relative to the transition section 122. In one example, the inlet 134 of the transition section 122 is free from obstructions that obstruct the flow of exhaust gas into the transition section.

In the illustrated embodiment, the transition section 122 includes a top wall 146, a bottom wall 148, a first side wall 150, and a second side wall (not shown) extending from the inlet 134 to the outlet 136. It is understood that the transition section 122 may be of other configurations. The top wall 146 has an interior surface 152 having a first curved (arcuate) segment, indicated at 154, generally adjacent to the inlet 134, a second curved (arcuate) segment, indicated at 156, generally adjacent to the outlet 136, and an intermediate segment, indicated at 158, between the first and second curved segments having a generally constant slope (i.e., a linear profile). Other curved wall configurations are within the scope of the present invention. For example, the interior surface may not have a second curved segment adjacent the outlet. Also, the interior surface may not have an intermediate segment, and the curved first and second segments may have abutting ends. Further, the intermediate segment may be curved without departing from the scope of the present invention. Any one (or all) of the other walls 148, 150 may have an interior surface designed according to the teachings set forth herein with respect to the top wall 146, or the other walls may have interior surfaces with a different, curved shape or a linear profile.

The first curved segment 154 generally increases in slope away from the inlet 134 and toward the outlet 136 (i.e., the first curved segment has a generally concave profile). The first curved segment 154 has a curvature (or radius of curvature) that is suitable for inducing a Coanda effect as exhaust gas flows from the inlet 134 toward the outlet 136, such that the flowing exhaust gas generally “follows” the curved interior surface upward, without substantial flow separation. The desired curvature (or radius of curvature) of the first curved segment 154, which causes the exhaust gas to generally follow the interior surface 152, may be dependent on such factors as the mass flow of the exhaust gas, velocity of the exhaust gas, the temperature of the exhaust gas, the size of the inlet, the size of the outlet, the length of the transition section, and the desired distribution and pressure within the transition section. A suitable curvature (or radius of curvature) of the first curved segment 154 to achieve the desired result may be determined by computational fluid dynamic (CFD) modeling, such as by using ANSYS CFX software, available from ANSYS, Inc. in Conansburg, Pa., or STAR-CCM+ software, available from CD-adapco in Melville, N.Y. As a non-limiting example, the radius of curvature of the first curved segment may be from about 5 ft to about 12 ft, more preferably from about 7 ft to about 10 ft, although the radius of curvature may fall outside these ranges, depending on the parameters set forth above.

Referring still to FIG. 4B, the second curved segment 156 generally decreases in slope away from the inlet and toward the outlet (i.e., the second curved segment has a generally convex profile). The second curved segment 156 has a curvature (or radius of curvature) that is suitable to reduce turbulence in and/or recirculation of the exhaust gas as the gas flow changes direction at the transition of the intermediate segment 158 and the second curved segment. Moreover, in the illustrated embodiment, the second curved segment 156 has a terminal end margin 160, interfacing with the auxiliary section 124, that levels off (i.e., extends generally horizontal) so that interior surface 152 of the top wall 146 at the terminal end margin of the second segment is generally flush with an upper interior surface 162 of the auxiliary section, which extends generally horizontal. This generally flush (smooth) interface between the transition section 122 and the auxiliary section 124 further reduces turbulence in and/or recirculation of the exhaust gas as the gas flows from the transition section into the auxiliary section. The desired curvature (or radius of curvature) of the second curved segment 156, which inhibits or lessens the exhaust gas from transitioning to substantial turbulent flow, may be dependent on such factors as the mass flow of the exhaust gas, velocity of the exhaust gas, the temperature of the exhaust gas, the size of the inlet, the size of the outlet, the length of the transition section, and the desired distribution and pressure within the transition section. The desired curvature (or radius of curvature) of the second curved segment 156 to achieve the desired result may be determined by computational fluid dynamic (CFD) modeling, such as by using CFD software identified above herein. As a non-limiting example, the radius of curvature of the second curved segment 156 may be from about 3 ft to about 6 ft, more preferably from about 4 ft to about 5 ft, although the radius of curvature may fall outside these ranges, depending on the parameters set forth above.

The intermediate segment 158 (FIG. 4B) has a slope that does not cause the flow of exhaust gas to “detach” from the interior surface 152. In other words, the slope of the intermediate segment 158 should be such that the flow of exhaust gas continues to “follow” the interior surface 152 as it transitions from the curved first segment 154 to the intermediate segment 152. The desired slope of the intermediate segment 158 may be dependent on such factors as the mass flow of the exhaust gas, velocity of the exhaust gas, the temperature of the exhaust gas, the size of the inlet, the size of the outlet, the length of the transition section, and the desired distribution and pressure within the transition section. The desired slope of the intermediate segment to achieve the desired result may be determined by computational fluid dynamic (CFD) modeling, such as by using CFD software identified above herein. In one non-limiting example, the slope of the intermediate segment 158 may be from about 45 degrees to about 90 degrees relative to horizontal, more preferably from about 60 degrees to about 80 degrees, although the slope may fall outside these ranges, depending on the parameters set forth above.

In the illustrated embodiment, a perforated plate 170 is received in the transition section 122 generally adjacent to the terminal end margin 160 of the second curved segment 156 and the outlet 136. The perforated plate 170 includes openings (not shown) that are generally larger than openings in conventional perforated plates. As a result, there is a reduced pressure drop using a single perforated plate with larger openings compared to conventional exhaust ducts. In other embodiments, the perforated plate 170 may be omitted, and the transition section 122 may be free from any perforated plate or other similar flow redistribution devices.

One non-limiting example of the transition section 122 illustrated in FIGS. 4A and 4B is disclosed hereinafter using suitable ranges for its dimensions. This exemplary transition section may be suitable for use in a gas turbine system that exhausts gas directly into the inlet 134 of the transition section, with a volumetric gas flow rate of about 11126 ACFS and a gas temperature of about 877 F. This exemplary transition section 122 may be suitable for gas turbines having other parameters. The inlet 134 of the transition section may have an open area of about 35.6 ft² (3.3 m²) and the outlet 136 of the transition section may have an open area of about 594.6 ft² (55.24 m²). The length L of the transition section 122, extending parallel to the axis A of the inlet, may be about 25 ft (7.6 m) The radius of curvature of the first curved segment 154 may be about 8.6 ft (2.6 m) and the radius of curvature of the second curved segment may be about 4.5 ft (1.4 m). The slope of the intermediate segment may be about 65 degrees relative to horizontal, and the intermediate segment may have a length of about 20 ft (6.1 m). FIG. 10 illustrates a streamline plot of a transition section constructed in accordance with the teachings of the embodiment illustrated in FIGS. 4A and 4B using ANSYS CFX software.

Referring now to FIG. 4, duct transition section 432 of another embodiment of the invention includes a gas turbine transition duct 420 having an upper curved wall 434. Upper curved wall 434 is curved in a non-linear manner to follow a path that assists in expanding turbine exhaust gas into larger duct area 433. Gas turbine exhaust duct 420 has inlet 418, and transition section 432. Transition section 432 has curved top wall 434, bottom wall 436, first side wall 438, and second side wall 440. Transitional section 432 additionally has an outlet end 442. In one embodiment, upper curved wall 434 has a first segment that increases in slope over a first distance, and a second segment that decreases in slope and then levels off to interface with expanded area 433 (i.e., the auxiliary section). The first and second segments abut, such that there is no intermediate section, as in the first embodiment (FIGS. 4A and 4B). In one embodiment, the curve followed by top wall 434 may be described by a third degree polynomial equation.

Referring now to FIG. 5, shown is another embodiment of a gas turbine transition section 532 of a gas turbine exhaust duct. Gas turbine transition section 532 has an inlet 518 and an outlet 542. In this embodiment, transition section 532 expands laterally to accommodate a duct having a width greater than the width of inlet 518 (not shown). Therefore, top wall 534 and bottom wall 536 may be straight and flat, while first side wall 538 and second side wall 540 curve outwardly. In one embodiment, the curves followed by side walls 538, 540 increase in slope with regard to a center line of transition section 532 over a length of transition section 532. In one embodiment, the curve followed by side walls 538 and 540 may be described by a second degree polynomial equation.

Referring now to FIG. 6, shown is another embodiment of a transition section 632 of a gas turbine exhaust duct 620. Gas turbine transition section 632 has inlet 618, a curved top wall 634, a bottom wall 636, a first side wall (not shown), and a second side wall 640. Transitional section 632 additionally has an outlet end 642. In one embodiment, the curve followed by top wall 634 increases in slope over a length of transition section 632. In one embodiment, the curve followed by top wall 634 may be described by a second degree polynomial equation.

Referring now to FIG. 7, shown is transition section 732 of a gas turbine exhaust duct 720. Gas turbine transition section 732 has inlet 718, curved top wall 734, bottom wall 736, first side wall (not shown), and second side wall 740. Transition section 732 additionally has an outlet end 742. In one embodiment, the curve followed by top wall 734 increases in slope over a length of transition section 732. In one embodiment, the curve followed by top wall 734 may be described by a third degree polynomial equation.

Referring now to FIG. 8, shown is an elevational view of transitional section 832 of gas turbine exhaust duct 820. Transition section 832 has an inlet 818, curved top wall 834 and curved bottom wall 836. First side wall (not shown) and second side wall 840 may be straight. Transitional section 832 additionally has an outlet end 842. In one embodiment, the curve followed by curved walls 834 and 836 has a slope that increases in magnitude with regard to a centerline of transitional section 832 over a first distance, then levels off to an interface with an expanded area (not shown). In one embodiment, curves followed by walls 834 and 836 may be described by a third degree polynomial equation.

Referring now to FIG. 9, shown is gas turbine transition section 932 of a turbine exhaust duct 920. Gas turbine transition section 932 has inlet 918, a curved top wall 934, a bottom wall 936, a first side wall (not shown), and a second side wall 940. Transition section 932 additionally has an outlet end 942. In one embodiment, curved top wall 934 has a straight portion adjacent to inlet 918, a portion where top wall 934 follows a curve with decreasing slope over a length of transition section 932, which results in a narrowing of transition section 932, then a portion of increasing slope. In one embodiment, the curve followed by top wall 934 may be described by a second degree polynomial equation.

Turbine transition ducts 432, 532, 632, 732, 832, and 932 may be used with gas turbine exhaust ducts of simple cycle units, units with emission reductions systems, or units with heat recovery steam generation systems or other turbine units. The curved transition ducts 432, 532, 632, 732, 832, and 932 are equally appropriate for expansion or contraction of gas streams.

In a preferred embodiment, after capturing the gas flow with the straight or convex surface, the subsequent duct surface of a duct wall, e.g., walls 122, 434, 538, 540, 634, 734, 834, 836, begins to curve away from the flow stream with an angle that begins small and that increases in magnitude for a length as the wall progresses. The turbine exhaust gas that was in contact with the straight duct wall continues to follow the curved wall as the gas turns away from the rest of the flow stream. Walls that follow a well designed curve will immediately reduce the pressure drop of the system while allowing for a shorter transition duct.

Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions, products, and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 

1. An exhaust duct for a gas turbine comprising: a transition section having a top wall, a first side wall, a second side wall, and a bottom wall, said transition section having an intake for receiving turbine exhaust gas and a relatively larger outlet area for interfacing with a larger duct area; wherein at least one of said top wall, said first side wall, said second side wall and said bottom wall has a first segment adjacent to the intake that defines a first curved surface that increases in slope toward the outlet area, and a second segment adjacent to the outlet area that defines a second curved surface that decreases in slope toward the outlet area and levels off at the outlet area to interface with the larger duct area.
 2. The exhaust duct set forth in claim 1, further comprising a larger duct area interfaced with the outlet area of the transition section, wherein the larger duct area includes an auxiliary section housing at least one of a catalyst, a silencer panel, and a perforated plate.
 3. The exhaust duct set forth in claim 2, in combination with a gas turbine, wherein the gas turbine is directly connected to the transition section at the intake.
 4. The exhaust duct set forth in claim 2, in combination with a gas turbine and a diffuser downstream of the gas turbine, wherein the diffuser is directly connected to the transition section at the intake.
 5. An exhaust duct for a gas turbine comprising: a transition section having an inlet for receiving turbine exhaust gas and a relatively larger outlet, the transition section including at least one wall defining an interior surface having a concave segment generally adjacent to the inlet and extending away from the inlet, and a convex segment generally adjacent to the outlet extending toward the outlet.
 6. An exhaust duct for a gas turbine comprising: a transition section having an inlet for receiving turbine exhaust gas, and a relatively larger outlet for interfacing with an auxiliary section housing an auxiliary device, wherein the transition section has an interior surface extending from the inlet to the outlet, the interior surface having a segment generally adjacent to the inlet that is curved to induce a Coanda effect in which said turbine exhaust gas is caused to flow along said curved surface and to expand for distribution of the turbine exhaust gas over the auxiliary device in the auxiliary section. 